Sequencing

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Transcript Sequencing

Scheduling
Introduction to Operations Management
1
What is scheduling
 In
a production system, it is the timing
and sequencing of the use of specific
resources in the system and is the final
step in the decision making process of an
organization before the actual
transformation processes begin.
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Scheduling Manufacturing Operations
JAN
 High-volume
FEB
MAR
APR
MAY
JUN
Build A
 Intermediate-
A Done
volume
 Low-volume
 Service
operations
Build B
B Done
Build C
C Done
Build D
On time!
Ship
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High-Volume Systems
 Flow
system: High-volume system with
Standardized equipment and activities
 Flow-shop scheduling: Scheduling for
high-volume flow system
Work Center #1
Work Center #2
Output
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High-Volume Success Factors
 Process
and product design
 Preventive maintenance
 Rapid repair when breakdown occurs
 Optimal product mixes
 Minimization of quality problems
 Reliability and timing of supplies
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Intermediate-Volume Systems
 Outputs
are between standardized highvolume systems and made-to-order job
shops
 Economic run size:
2DS
p
Q0 
H p u
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Scheduling Low-Volume Systems
 Loading
- assignment of
jobs to process centers
 Sequencing - determining
the order in which jobs will
be processed
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Loading
 Gantt
chart - used as a visual aid for
loading and scheduling
Work
Mon. Tues.
Center
1
Job 3
2
Job 3
3
Job 1
4
Job 10
Wed.
Thurs.
Fri.
Job 4
Job 7
Job 6
Job 7
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Assignment Problem
Assigning jobs to workers. There is
a cost associated with a worker
completing a certain job. The
objective is to finish all the jobs by
the workers so that the total cost is
minimized.
Jobs
Workers
An optimal solution can be found
by the Hungarian
Method.
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Sequencing
 Sequencing:
Determine the order in which
jobs at a work center will be processed.
 Workstation: An
area where one person
works, usually with special equipment, on
a specialized job.
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Sequencing
 Priority
rules: Simple heuristics
Everything is
used to select the order in
#1 Priority
which jobs will be processed.
 Job
time: Time needed for
setup and processing of a job.
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Priority Rules
 FCFS
 SPT
 DD
 CR
 S/O
 Rush
- first come, first served
- shortest processing time
- due date
- critical ratio
- slack per operation
Top Priority
- emergency
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Two Work Center Sequencing
 Johnson’s
Rule: technique for minimizing
completion time for a group of jobs to be
processed on two machines or at two
work centers.
 Minimizes total idle time
 Several conditions must be satisfied
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Johnson’s Rule Conditions
 Job
time must be known and constant
 Job times must be independent of
sequence
 Jobs must follow same two-step sequence
 Job priorities cannot be used
 All units must be completed at the first
work center before moving to second
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Scheduling Service Operations
 Appointment
systems
– Controls customer arrivals for service
 Reservation
systems
– Estimates demand for service
 Scheduling
the workforce
– Manages capacity for service
 Scheduling
multiple resources
– Coordinates use of more than one resource
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Service Operation Problems
 Cannot
store or inventory services
 Customer service requests are random
 Scheduling service involves
– Customers
– Workforce
– Equipment
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